This invention is concerned with a shaft sealing technique for a mechanical seal.
Heretofore, a mechanical seal used in a shaft sealing device frequently used a floating sheet of the type in which the floating sheet is moved uniaxially by the elastic repulsive force of an O-ring fitted over the floating sheet to bring its sliding surface into abutment. As shown in FIG. 1, this floating sheet (10) is such that a sliding surface (12) is integrally molded at one end of an annular base portion (14), and an O-ring is fitted over a tapered peripheral groove (16) formed on the outer periphery of the annular base portion (14). However, the above floating sheet (10) is formed by casting and, in order to improve the wear resistance of the sliding surface, it usually is subjected to heat treatment such as hardening. Therefore, the dimensional accuracy is difficult to attain and the after treatment is not easy, for which reason its manufacture is extremely difficult. As a result there have been variations in the quality of the resulting product. Further, due to deformation or dimensional error of the floating sheet (10), particularly the tapered peripheral groove (16) which serves as an allowance for compression of an O-ring becomes non-uniform, resulting in the sealing performance being deteriorated. In view of and in an effort to remedy such drawbacks there have been proposed such constructions as illustrated in FIGS. 2 and 3 in which retainer (18) and slide ring (20) are separately formed and, after machining the slide ring (20) by means of a lathe or the like, both are combined together integrally. In the case of a floating sheet (22) shown in FIG. 2, the slide ring (20) and the retainer (18) are integrated together by the so-called "caulking method," that is, the slide ring (20) is fitted into one end of the retainer (18) and then an outer periphery (24) of the retainer (18) is bent into pressure contact with an outer periphery (26) of the slide ring (20) airtightly throughout the circumference. And in the case of the floating sheet (28) illustrated in FIG. 3, the slide ring (20) and the retainer (18) are integrated together by the so-called "shrinkage fit method" wherein a fitting stepped portion (30) formed at one end of the retainer (18) is subjected to thermal expansion by heating, and the slide ring (20) is fitted to the so-expanded fitting stepped portion (30) and both are integrated together airtightly at normal temperature. In both cases of the floating sheets (22) and (28), however, since the slide ring (20) and the retainer (18) are each manufactured individually and then brought into integration, the magnitude of respective dimensional errors in machining is likely to affect directly the stress on the slide ring (20), resulting in that a plane strain is produced on the sliding surface (12) of the slide ring (20) so that good airtightness is not attained. The floating sheets (22) and (28) involve such a problem. In the former floating sheet (22), the magnitude of caulking force applied throughout the circumference of the outer periphery (24) of the retainer (18) has influence upon the magnitude of the pressure-bonding force, and the difference in distribution of such pressure-bonding force causes a strain in the slide ring (20). The latter floating sheet (28), shown in FIG. 3, is also disadvantageous in that the machining error between the outer periphery of the slide ring (20) and the fitting stepped portion (30) of the retainer (18) produces a difference in the pressure-bonding force at the time of shrinkage fit, resulting in the slide ring (20) being deformed or broken. Such being the case, there has been a demand for a mechanical seal provided with a floating sheet having a high sealing characteristic free from plain strain of the sliding surface (12), and for a method of making such a floating sheet.